The display apparatuses using liquid crystals are lately in wide spread use, but these are not the best in such properties as energy-saving or brightness, since a liquid crystal display apparatus uses backlight in principle. For this reason, the research and development are widely proceeding for a solid state light-emissive display apparatus, aiming to realize high brightness, energy-saving, flat type, and high reliability rather more than liquid crystal.
As an existing solid state light-emissive display apparatus, there is EL(Electro Luminescence) display apparatus. EL display apparatus is composed of pixels each of which has a semiconductor layer including light emission center atoms and insulator layers sandwiching said semiconductor layer. As a light emission center atom, such elements that emit visible fluorescence, for example, Mn or rare earth elements are used, and as a semiconductor layer, such semiconductors that have larger band gap energy than visible light, for example, ZnS or else are used, and as insulator layers, such insulators that have a property which prevents dielectric breakdown of said semiconductor layers, for example, thin films of SiO2 or Si3N4 are used.
EL display apparatus emits light as following, electrons in a semiconductor are accelerated by high electric field imposed through insulation layers, the accelerated electrons collide to light emission center atoms to be excited, and the excited light emission center atoms emit fluorescence light. Therefore it is the specific feature of EL display apparatus that electric energy directly converts to light energy.
However, there are problems such that light emission efficiency is low and dielectric breakdown tends to occur, because considerably high electric field (106 V/cm or higher) is necessary to accelerate the electrons to such a high energy state (hot electron state) to emit EL light against the energy dispersion by phonon scattering. There are also such EL display apparatuses using organic materials as the semiconductor layer, but they also have problems such that emission efficiency easily becomes lower as organic materials are unstable and readily deteriorate.
There are also FED (Field Emission Device) display apparatuses as the display apparatuses to generate fluorescence by colliding and exciting light emission center atoms by accelerated electron (ballistic electron). However, an FED display apparatus has its problems such that, though it can emit light at relatively low electric field, it requires vacuum space and hence it can not be made to a flat and all-solid state type, since it emits out electrons into vacuum by using a field-emission type electron gun and accelerates them in vacuum.